Digital Measuring System for Monitoring Motor Shaft Parameters on Ships

The robust measuring system for the continuous monitoring of the ship motor shaft average torque, power, and rotational speed was developed and tested. The system was designed for permanent installation in ships under realistic working conditions. The strain gage sensor is employed to measure the torque, whereas the shaft rotational speed is measured by the inductive proximity switch. The strain gage signal conditioning circuit design was highly simplified by using a high-resolution SigmaDelta A/D converter (ADC). Such an approach minimizes the overall number of analog components and the input measuring chain errors. A contactless power transmission subsystem was developed based on the specifically designed rotary transformer operating at low frequency. Strain measurement results are transmitted over the near-field low-frequency capacitive link by using a specifically designed communication protocol based on the digital modulation principle. The receiver microprocessor-based unit processes the measured data and transmits the results to the monitoring human-machine interface over some commonly used industrial analog and digital communication protocols. The principal advantages of the novel measuring system design over some state-of-the-art commercial solutions are simplicity, higher accuracy, stability, reliability, simplified calibration procedure, and contactless signal transmission and processing completely in a digital form, which, hence, reduces the most common shortcomings of similar analog-based systems.